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The Water D/H Ratio in Molecular Outflows in Orion BN/KL

The Water D/H Ratio in Molecular Outflows in Orion BN/KL. Shiya Wang Astronomy Department, University of Michigan Edwin A. Bergin (U. of Michigan) René Plume (U. of Calgary). Midwest Astrochemistry Meeting, Nov. 7-8, 2008. ISM(ices). Comets(1AU). 100 2 - 20 4 - 24 3 - 10 2 0.4. 100

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The Water D/H Ratio in Molecular Outflows in Orion BN/KL

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  1. The Water D/H Ratio in Molecular Outflows in Orion BN/KL Shiya Wang Astronomy Department, University of Michigan Edwin A. Bergin (U. of Michigan) René Plume (U. of Calgary) Midwest Astrochemistry Meeting, Nov. 7-8, 2008

  2. ISM(ices) Comets(1AU) 100 2 - 20 4 - 24 3 - 10 2 0.4 100 5 - 7 3 - 20 0.3 - 5 0.2 - 1.2 0.2 H2O CO CO2 CH3OH CH4 OCS Langer et al 1999, PPIV Interstellar and Cometary Ices

  3. H2DO+ O O HDO H2O H3+ HD H2D+ H2 OH OD H3O+ Deuterium Fractionation of Water HDO/H2O > HD/H2 ~ 3 x 10-5 O e- e- e- HD H2 High T Low T cosmic ray O e- e-

  4. Water Origin in Molecular Outflows Orion BN/KL • High-T shock chemistry • Supersonic flows compress and heat the surrounding material and change the chemistry • shocks with velocities between 15 • and 30 km/s will produce large • amounts of water vapor • (Kaufmann & Neufeld 1996) • O + H2 OH + H • OH + H2  H2O + H • Grain surface evaporation • Grain-grain collisions and sputtering in shocks can vaporize mantles

  5. CSO HDO 464 GHz Emission in Orion BN/KL TA* (K) VLSR (km/s) Plateau (18km/s flow): X(H2O) ~ 4 x 10-6 (Persson et al. 2007) HDO/H2O ~ 0.005 Offset in Arc-Seconds

  6. 3 Stage Chemical Model Stage 1 Stage 2 Stage 3 Pre-Shock Tgas = Tdust = 10 - 30 K 106 years Shock vs = 10 - 40 km/s Tgas= 500 - 3000 K Tdust = 10, 500 K 100 years Post-Shock Tgas = Tdust = 30 K 106 years • constant density • visual extinction Bergin, Neufeld, & Melnick 1998 Kaufmann & Neufeld 1996

  7. Outflow age ~ 3000 years with 20 km/s, 0.04pc  shock <----- -----> post-shock  

  8. Outflow age ~ 3000 years with 20 km/s, 0.04pc   shock <----- -----> post-shock 

  9. Summary • Enhanced water abundance will persist for ~105 yrs, whereupon water freezes onto grain surfaces • Two cases: (1) all the shocked water is produced by shock chemistry via gas-phase reactions of O and OH with H2 (2) all atomic oxygen is locked on grains in the form of H2O, which then evaporates from the grain surfaces when shocked. • Observed water abundance in Orion BN/KL low-velocity outflows can be produced in shocks (with shock velocity ~20 km/s and preshock gas temperature ~ 20 K), without grain evaporation contributions

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